The authors examine the effects of undergraduate research experiences on key steps in the path to medical school, considering the case of an undergraduate research experience (URE) offered to first-year students that also might influence performance in large introductory science courses. Using a historical dataset of 15,000 first-year students, logistic and linear regressions were performed to better understand the influence of early UREs on different measures of college success. Immediate effects of an early URE on second-year course performance and very large effects on second-year retention are demonstrated. There also are delayed effects on taking the MCAT and medical school acceptance. Results demonstrate the importance of early UREs and their role in STEM student persistence.